Control of crystal development in refractory metals



Patented Get. l2, 1926.

NiTED l 'itozz @FH Eo WILLIAM BENJAMIN GERO, OF EAST ORANGE, NEWJERSEY,YASSIGNOR TO WESTIN G- HOUSE LAMP COMPANY, A CORPORATION OFPENNSYLVANIA.

CONTROL OF CRYSTAL DEVELOPMEN IN REAFRACTORY METALS.

Application filed September 15, 1922. Serial No. 588,364.

This application is a continuation-impart of my copending applicationSerial No. 437,035, filed Jan. 13, 1921, method of manufacturingmetallic filamentary material, and assigned to the Westinghouse LampCompany.

' The invention relates to the manufacture of refractory metals suitablefor incandescent electric-lamp filaments and the like, and moreparticularly to the control of the crystalline development of tungstenby the addition of slected materials. U

An object of my invention is the production of filamentary materia-l oftunvsten, molybdenum or the like to which salts of other metals, suchcasthe alkali and alkaline-earth metals, have been added to control thecrystal development thereof. Y Another object of my invention is thedevelopment of refractory metal wire or fila-` mentary material with acrystalline structure which is fixed and not subject to fur' therdevelopment when used in an incandescentjelectric lamp and the like,whereby consequent sagging, twisting or other dis` tortion is avoided toa large extent. f,

A further object of my invention is the predetermination of the shapeand arrangement ofthe crystals forming a tungsten filament or the likeby the addition to the material or oxide, from which the same is tobemanufactured, of a small proportion of one or more of the alkali oralkalineearth `metals or a compound or compounds of the alkali oralkaline-earth metals, the additive substance selected depending on thekind of crystallinestructure desired in the metal when manufactured'into a coherent,

form, which is determined bythe use to which thefllament isto be put.

A still further object of my invention is the production of wire,composed of metal of the tungsten-lclass, responsive to shortheat-treatment, whereby a grain or crystal structure may beconvenientlydeveloped therein, in which equilibrium is established, that is, wherethere are no internal stresses due to growth or rearrangement of thecrystals, whereby the wire will not sag,

twist or otherwise distort even when used under severe conditions.

Other objects and advantages will be made apparent as the descriptionproceeds.

It has been discovered by experimentation that the crystalline structureof refractory metallic material such as tungsten may be modified by theAaddition thereto or incorporation therein of certain substances whereiby the tendency of filamentary tungsten and the like to sag andotherwise distort, when highly' heated, maybe overcome to 'a greatextent. It has beeiirfound that the amount of Isag and other distortionin refractory rpurpose are compounds of lithium,V sodium,

potassium, rubidium, caesium, beryllium, strontium, calcium, barium, andother metals'.

Metals especially adapted for controlling i crystalline development havebeen found to be alkali and alkaline-earth metals'which appear topromote the crystalline development of refractory metallic material,whereas certain other materials appear to retard such crystallinedevelopment. I conclude, therefore, that elements which form oxidesAthat are generally classified as non-reducible in hydrogen, may bedivided into two general classes, those which oppose or repress`crystallization when added to tungsten or other similar refractorymetal and those that promote such crystallization. Examples of theformer are\ thorium and aluminum. whereas .examples of the latter arethe alkali and alkaline-earth metals.

Itis to b e understood that this effect takes place when a filamentcontainin such an admixture is heated or anneale Furthermore, eachmaterial exertsl a different eiTect on the character of the resultantcrystals. This effect appears to be a controlling factor in determiningtheshape and'contour of the crystals, the direction of maximum growth,

the speed ofy crystallization and the germi# nation point. Consideredfrom a practical stand oint, the Acharacteristics of the crystals of) afilament or wire can bey predetermined before the metal is produced bycontrolling the additive 'material or materials.

Certain factors, such as impurities inthe class of substances whichoppose the tendency to crystal growth, 'may interfere with tassiumthedevelopment of the structure, characteristic of any of thesematerials. .For example, metal may have been treated with potassiumycompounds and normally, one would expect potassium characteristics.A If,however, an 'impurity such as thoria is present in sufficientquantities, the crystal structure may be considerably modified. Somematerials, such as compounds of lithium, exert a strong effect, whileothers, such as sodium and pocompounds, exert definite but weakerefects.- Impurities will not interfere with the development ofcrystalline struc-` ture, by materials like the formeras much as theywill with that of the latter. When the impurity is a compound of analkali or alkaline-earth metal, in certain proportions, the crystallinestructure produced maynot be characteristic of either one, but theresult of the modifying effect of the impurity on the additive material.

Different compounds of the same metal for example, either lithiumchloride or lithium nitrate, give the same crystalline characteristicstructure of lit ium material. This indicates thatv probably themetal,and not the associated radical, determines the ultimate structure of thewire. There is every reason to believe that compounds of eacl element orat least ea metallic element, when introduced into refractory metal suchas tungsten, will exert a definite effect upon the crystalline habits ofsuch metal. This fact is characteristic of the material introduced and,for the same'material, the effect is the same unless offset by otherfactors, vsuch as impurities whichoppose this effect. All materialswhich are excluded from the crystalline formation and segregate at thegrain lboundaries havesimilar effects on the crystalline structure oftungsten and the like, that is, they oppose crystal growth and promotethe formation of fine grains of uniform size. any material may change'the crystalline habits of a tungsten filament, for example, it verylikely must, in some way, take -part 1n the crystalline formation. Mostof the materials of this class such -as the alkali and alkaline-earthmetals show a fairly low volatilization point so that considerable ofthe .material added will undoubtedly volatilize during heat-treatment ofthe refractory metal. Some, however, it is thought,'must combinewith thetungsten metal or oxide with the f rmation of a compound or'compounds mrmaterial a d, in this way, some of said material is retained in theingot or slug during the rtreating operation.A Such combinations arethen probably absorbed in the crystals and exert. their characteristiceffect onvthe 'form and size thereof. The additive matetreatment.

Conversely, in order that' e refractorythanthe additive The,` additivematerial not only affects the .4

crystalline development of the finished product when introduced into theoxide of the refractory metal before reduction, but the same introducedinto the' powdered metal 70 or even the wire itself would probablyaccomplish the desired result.

My invention, by referring to the accomp in which will better be'understood Fig. 1 vrepresents a micro-photographv showing an etchedlongitudinal Section of a tungsten filament magnified 200 diameters,said filament being approximately 7 mils in diameter and being preparedwith the addi' 80 Jtion of a small proportion of @compound of lithium;

Fig; 2 is a similar longitudinal sectional view of a filament preparedwith the addition cfa small amount of 'a compound of 3 5 strontium;

Fig. 3 is a similar view of a lament to which has been added a compoundof caesium during the process of manufacture;

Figs. 4 and 5 are similar views of ila- 90 ments to which have beenadded during the process of manufacture a compound of potassium; and,

Fig. 6 is a similar-view ofa filament to been added during the processof 9 which has manufacture a compound of rubidium.

It will be noted that'the addition of ,lithium to the material used forpreparing arefractory metal filament causes the lformation of largecrystals fairly regular in size andshape, as shown in Fig. 1. Thesecrystals appear to be largely hexagonal, and wire of such crystallineformation appears to be specially adapted for the larger sizes of inl(candescent electric lamp filaments.

Strontium and caesium havecrystal effects as illustrated in Figs. 2 Aand3 but the crystalline formation is'very similar to that obtained by theuse of lithium compounds as will be notedA by comparison with Fig. 1. l

Potassium, on the other hand, appears to promote the development ofelongated interlocking crystals irregular in size and shape 1 asrepresented in Figs 4 and 5. Such a formation is best adapted l' forfilaments of l the smaller sizes. By referring to Fig. 6, it will benoted that rubidium gives characteristic crystalline effects, similar.to those obtained with the use of potassium, aswill be observed bycomparing Fig. 6 with Figs. 4 and 5.

The following experiment was performed to compare the relative effectsof potassium, sodium and lithium as additive or doping material in theVformation ofrefractory metallic. lamentary material of various sizes.k32 kgs. of regular purified tungstic oxide was divided into fourportions of 8 kgs. each, one portion .being reduced without the. ad-

h'dition of any crystal-controlling material l anying drawing i 7 Add dI Illlent gf] e a me a Metal' material. oxide by weight.

All batches were heated to about 500 to 600 C. and reduced by the sameprocess. The metal was pressed 1n 220 gram, l@ inch slugs, 16 incheslong, treated and retreated on the same schedule. The treating currentwas 1600 amperes for 12 minutes and the retreating current was 80% ofthat calculated for causing fusion of the rod or slug, then 160 milsindiameter.

The oxide was so prepared as to be originally free from .any materialswhich would effect its crystalline structure; therefore, the structureobtained from the metal #1 is the normal structure for pure tungsten or,at least,l for that of tungsten produced from the oxide used. T n, bygiving all the same treatment and omparing that to which the alkalimetal compounds were added with pure tungsten, effect ofthe variouscrystal controlling materials. was attained. All precautions werel takentoinsure parallel treatment for all slugs, such as treating at the sametime and using the same smoothingV die before re-` treating. Thefollowing tablel shows the" results obtained, so far as the grain delvelopment is concerned.

Grain cou/nt.

Initial, before swag- Rss-treated, after ing. swaging.

Metal. l Variation Variation between between Count. maximum Count.maximum and miniand minimum. mum.

Per cent. s Per cent. 1050 12 400 2340 27 425 16 2040 165 56 2690 3 59upecime-ns are reversed. Theorder of grain `ount is decreasing'with theatomic weight ladditive.' materials,

. drawings. As shown yinterrupted band of a method of evaluating theofthe'vadditive'metal, the grain percentage variatlon being increasingfrom metal. 2

to metal 4, instead ofdecreasing as was i the case on thev initialtreating. These facts form conclusive evidence thatl the various y.

even at this early stage in the process, have exerted a characteristiceffect upon the tungsten. This effect mayv be traced throughout theprocess. The char` acteristics developed by some of these Ina-- terialsannealed as drawn wire about '7 mils in diameter are illustrated in theattached in Fig. 1, for a drawn filament, the -lithium-treated materialis particularly distinctive in the size of crystals and thefairlyregular boundaries thereof.

A practical application of the above described discovery may beillustrated by the production of iilamentary material for motion pictureor projector lamps. Such lamps arelconstructed of four coiled definitedistance froin each other. The images of the coiledsections arereflected betweenthe adjacent sections by a mirror suitably placed,giving the edect of `ran un# light when projecting on asceen.

filamentary sections parallel to each other and set at a- Then afilament operates at the high tem- V perature which is required insuchlampsV it is frequently found that the portions'of the coils willbecome separated, giving the phenomenon of sagging. Another defectAwhich develops and disturbs the distribution of light 1s known astwisting, that is, a displacement of one section of a coil withrespectto another about an axis midway beV tween, and parallel to, thesections. A

Twlsting may take place in bther ways `but this is the most prominentform. Any

displacement of any section of the coil, as described above orotherwise, which inter- 'feres with. the distribution of light makes thelamp ineffective and necessitates its replacement. v v

Experience has demonstrated that it 1s extremely dicultto obtain afilament which will resist the development of all these defects whenoperated at high temperature and therefore, it is to be considered thatunusually severe conditions are improved upon a filament for motionpicture lamps of the aforedescribed incandescent typ.l Ingenious deviceshave been devised in attempts to eliminate the distortion of suchfilaments. Among these may be mentioned, special anchors which operateto prevent twisting, also winding adjacent coils in reverse directions,so that the tendency to'twist will' be neutralized between any twoadjacent coils. These expediente have the effect of increasing'cost andcomplicating the process of manufacture and frequently proveineffective. ,V

Wire or filament has been produced according to my invention, whichfulfills all the conditions necessary for a motion-picture lamp and isresistant to both sag and twist. l

The following method is an example of how such wire may bevproducedlbutit is obforth, and it should be understood that the lithium compound maybe replaced by one or more compounds of metals such as cacsium,strontium, calcium and barium, with or without other material, such asalkali-metal compounds, for the development of crystal structuressimilar to that developed with the use of lithium, asy will beappreciated by comparing Figs. 1, 2 and 3.y

YIt has been found that purified tungstic oxide` varies in itsproperties according to the method employed in its purification. Thesevariations are apparent to those familiar with the material, and mayshow as differences in density, particle size or chemical activity.Generally, oxides prepared by the usual processes of precipitating asoluble salt of tungsten in hot acids have given good results and I-viveone method for purifyin oxide which will also give a'product satisactory for the purposes of my invention. j

68 kgs. of commercial tung'stic acid may be dissolved in a mixture of64= liters of ammonia specific gravity .9, and 160 liters of distilledwater. After the residue is settled the solution is filtered. Thissolution may be distributed in stoneware dishes of `approximately 40gallons capacity. Concentrated hydrochloric acid, of specific gravity1.19 may be added slowly through a 1/8 inch orifice to precipitatepara-ammoniumf tungstate, which is thoroughly washed and dried. Theammonia in the compound may be eliminated either by heating, to atemperature not exceeding 1300o F., or by digesting inacids. The oxideremaining will be found to have been purified, by the aforedescribedoperations, sufficiently for making wire according to my' invention.

Lithium nitrate may be incorporated into the purified tungstic oxide sothat the content therein is about .1% of lithium oxide by weight.`(About .05% weight). This mixture is preferably dried `at a temperaturesufficiently high to drive off the oxides of nitrogen. The dried andpowdered tungstic oxide containing lithium be reduced to powdered oxidemay then to some knownv method.

metal according Other, methods may the tungstic oxide containing theadditive material. However, the following method is preferred.

*200 grams of the purified tungstic oxide of lithium by v be used forreducing may be placed in a shallow container 3() inches long, made bv'bending a strip 2 inches wide formed o any desired common metal suchas copper, iron, or the like into the shape of a semicircle and closingboth ends. The material maybe spread evenly throughout this container,which may then be passed through a tube 1% inches in diameter, at aspeed of approximately30 inches per hour.` Approximately 20 cubic feetper hour of dry hydrogen gas is passed through this tube, its'direetionof ow being the reverse of the direction of travel of the oxide. Thetube 4consists of a heated sectionv 6 feet long, with extensions on-each end' to provide for introducing the oxide and removing the metalrespectively.

A temperature gradient should be established along the tube, with thehighest temperature near the exit end, such that the reduction to themetal proceeds slowly along its length, passing through the variousstages, as indicated by the various oxides formed. The temperatureshould .not be higher than is necessary to reduce the metal. I find thatit is often advisable to divide the process into two steps and, insteadof taking control the temperature such that a small quantity of brownoxide is still present with the reduced metal. The metal powdercontaining such oxide is then mixed with an equal quantity of theoriginal oxide and reduced again under identical condit1ons,except thatthe temperature is raised sufficiently to effect complete reduction. l

The metal powder produced, may then be pressed into slugs, treated,worked and drawn, that is, manufactured into a v.coherent body or wireby the usual process. Such wire, when annealed or lighted up, in aninert environment,'for example, as an incandescent lamp filament, willdevelop a crystal-structure, characteristic treated material.Furthermore, this wire is resistant to both sagging and twisting.

Lamps having filaments of various types including lithium-treatedmateria were made up according to Iregular test practice, that is, a twosection coil was mounted on leads wit out bottom anchors and ported aeight of 17 grams, thereby imposing unusually severe qonditions on thefilaments. Lamps)of this type, with filaments 25 mils. in diameter, 31amperes in an inverted position for 10 hours. v At the end of this time,the amount of sag and twist was noted and the-results are as follows:

Bas. Twist.

Per tml. Lithium-treated wire 13. 6 Nono. Thor wir 108 30 of lithiumwereburned) at 3 due to re-arrangement Although a slight amount of sag isshown for the lithium-treated Wire, it should be understood that it iscaud by the unusually severe conditions imposed on said Wire, whichmagnified or exaggerated the sag in the Wire and are sosevore that eventhe best non-sag Wire, sags under tlies'e conditions. The results shownwere selected at random and are representative of several similarcomparisons. Lithium-treated wire, besides developing a characteristiccrystal structure,v is responsive to heat treatment. Vhen heated for anextremely short period, in an inert environment, its grains developfully and an equilibrium is established. This property may explain itsresistance to twist, as its normal structure is developed immedi' atelywhen first lighted up. The filament is, therefore, in a state ofequilibrium and there are no internal stresses of crystal grains to,cause the filament to distort or twist.

It will be appreciated that, according to my invention, the crystal"structure of a filament is predetermined by properly selecting y theadditive material.

rubidium, and, to a smaller extreated metal gives material Potassium,tent, sodium l which tends to develop large grains which extend alongthe axis of the Wire and these materials each give a characteristic butsimilar crystalline development and reference' is made to Figs. 4, 5 and6.

Lithium treated material, however, develops large grains of regularcontour and fairly uniform size and, when prepared'in filamentary formof fairly large diameter, for example, larger than .about l0 mils, willneither sag substantially nor twist, even under seyere conditions. 'Itis, therefore, possible to manufacture tungsten Wire or Wire of otherrefractory metals of various characteristics from the same supply ofpurified oxide simply by the addition of selected materials.

Although Vthe example given for preparing lithium treated Wire statesthe use of .1% of lithium oxide as the amount found to work best, Ido'vnot Wish to be limited to this figure, but it is thought that, forthe best results, the quantity should not be less than about .02% orgreater than about 11/2% by Weight. (From about .01% to about .75% oflithium by weight). l do not Wish to be limited to the use of a singleadditive material for producing the desired results, as l have foundthat mixtures may be used to advantage, with one material modifying theeffect of the other.

Although I have described what I now consider the preferred means ofpracticing my invention it is to be understood that the same are merelyillustrative and that my invention is only limited by the scope of theappended claims. f

sae

What is claimed is:

l. The method der from which may be produced non-sagging andnon-offsetting filaments having predetermined grain or crystal structurewhich comprises mixing tungsten oxide, free from compounds deleteriouslyaffecting the desired crystal development and a predetermined quantityof at least one compound of an alkali or alkaline earth metal capable ofpromoting the grain or "crystal structure desired to be produced,partially reducing the mixture and mixing with said partially reducedmixture an additional quantity ofthe first mixture and then completelyreducing said last mentioned `mixture to obtain a mixture vof tungstenmetal and a compound containing tlie alkali 0r alkaline earth metal.

2. The method of preparing tungsten filaments having a grain or crystalstructure fairly regular'in size and shape, Which comprises mixingtungsten oxide free from c ompounds deleteriously affecting the desiredcrystal structure, and a definite and determinable quantity of acompound or compounds containing alkali or alkaline earth metals capableof promoting a structure consisting of crystals or grains fairly regularin size and shape, reducing said mixture to tungsten metal and acompound or com-v pounds containing the added alkali or alkaline earthmetals, sintering and mechanically Working the sintered metal tolfilament size.

3. Themethod of preparing tungsten filaments having a grain or crystalstructure fairly regular in size and shape, which comprises mixingtungsten oxide free from compounds deleteriously affecting thedesired.crystal structure, and a definite andv determinable quantity ofcompounds containing alkali and alkaline earth metals capable ofpromoting a structure consisting of crystals or grains fairly regular'insize and shape, reducing said mixture to tungsten metal and compoundscontaining the added alkali and alkaline' earth metals, sintering andmechanically `Working the sintered metal to filament size.

4. rlhe method of preparing tungsten filaments having a predeterminedgrain or crystal structure Which comprises mixing tungsten oxide, free?from compounds deleteriously affecting the desired crystal development,and a predetermined q uantity of a mixture of compounds of alkali oralkaline earth metals capable of promoting the grain or crystalstructure desired to be produced, partially reducing the mixture andmixing vWith the said partially reduced mixture an additional quantityof the first mixture and then compietely reducing said last mentionedmixture to obtain a mixture o f tungsten metal and a compound containingthe of preparing tungsten powy alkali or alkaline earth metals,pressing, f

sintering', and mechanically working said sintered material to lamentsize.

5. Themethod of preparin tungsten laments having a predetermine grain orcrystal structure which comprises mixing tungsten oxide, ree fromcompounds deleteriously ailecting the desired crystal developmment, anda predetermined uantity of a mixture of compounds of alkah and alkalineearth metals capable of promoting the grain or crystal structure desiredto be produced, partially reducing the mixture and mixing withtthe saidpartially reduced mixture an additional quantity of the first mixtureand then completely reducing said last mentioned mixture to obtain a.mixture of tungsten metal and compounds containing the' alkaliandalkaline earth metals, pressin sinter Iing and mechanically workingsai sintered material to filament size.

6. The method 'of preparing tungsten powder from which may be producedfilaments possessing a grain structure resistant to sagging and twistinwhich comprises mixing a tungsten oxi e free from compoundsldeleteriously ecting the desired crystal development ith a predeterminedquantity of a compound or compoundscontaining lithium,` strontium,calcium or caesium, partially reducing said mixture, adding Nafquantityof the first mixture to the partially reduced mixture and thencoinpletely reducing the same to obtain a mixture of tungsten metal anda compound or compounds containing lithium, strontium, calcium orcaesium.

7. The method of preparing ilamentary material having a predeterminedcrystal orv grain structure which is resistant to sagging andoisettinwhichcomprises mixing tungsten oxide ee from compounds deleteriouslaiectinr crystal development and a pre eterminedb quantity of at leastone compound of an alkali or alkalinevearth metal capable ofpromotingethe grain or crystal structure desired to -produced,partiallyreducing the mixture and mixing with the said partially reducedmixturean additional quantity of the first mixture and then completelyreducing said last mentioned mixture to yobtain a mixture of tungstenmetal and the compound containing the additive material, pressinsintering and working said material to t e desired size and shape.

8. The method of preparing filamentary material having a' predeterminedcrystal or grain structure which is resistant to sagging and oisettingwhich comprises mixing tungsten oxide free` from com unds deleteriouslyaffecting crystal deve opmentand a redetermined uantity of at least onesalt oan alkali or of 'promoting the ain or crystal structure desired tobe p uced, partially reducing the mixture andmixing with the saidpataline earth metal'capable mg moans tially reduced mixture anadditional quantity of the irst'mixture and then completely 's reducingsaid last mentioned mixturetoobtain a mixture of tungsten metal and acompound containing the additive material, pressing, sinterin rial tothe desire size and shape.

and workingsaid mate- 9. The method of preparing ilamentary l materialhaving a predetermined crystal or crystal development and` l a definltequantity of a mixture of compounds of and alkali or alkaline earth metalcapable of promoting the grain or crystal structure desired to beproduced, partially reducing the mixture and mixing with the saidpartially reduced mixture an additional quantity ofthe first mixture andthen coinpletely reducing said last mentioned mixture to obtain amixture of tungsten metal andy a compound. containing the additive imaterial, pressing,

sintering and working said material to the desired size andrshape.

10. The method of preparing lilamentary 'material having a crystal orgrain structure which is resistant to sagging and twisting vwhichcomprises mixin a tungsten oxide free from compounds de eteriouslyaffecting ,crystal development- 'and a compound containing atleast oneof the metals, lithium, csium, calcium, or ducing the mixture, squantity of the first mixture to the partially reduced mixture,substantially completely reducing the last mentioned mixture to obtainaA mixture of tungsten metal and a compound. containing the additivematerial, pressing, sintering and working said material to the desiredsize and shape. 4 s,

11. The method of preparing tilamentary material having a crystal orgrain 'structure which is resistant to sagging and twisting whichcomprises mixing tungsten oxide free `from compounds deleteriouslyaffecting crystal development anda compound contalning lithium,partially reducing the mixture, adding an additional uantity of thefirst mixture to the partia y reduced mixture, substantially completelyreducing the last mentioned mixture to o tain a mixtu-r'e of tungstenmetal and a compound containing the additive material, pressing,sintering and working said material to the desired size and shape.non-twist wire which comprises adding to 'a refractory metal oxide freefrom compounds deleteriously aectingcrystal forniation, a small amountof-a compound containatleast one ofthe alkali or alkaline earth metals,lithium, strontium, calcium or caesium, and reducing the mixture to. ob

tain a of the refractory metal and 12. The method of making non-sag andstrontium, partially ref adding an additional l1) ing said therefractory a compound containing the additive material, and thereafterfabricating said powder into wire by sintering and mechanically Workingthe sintered metal.

13. The method of making non-twist wire which comprises adding to arefractory metal oxide free from compounds deleteriously affectingcrystal formation, a small amount of a mixture of compounds containingalkali or alkaline earth metals, such as lithium, strontium, calcium orcaesium, reducing the mixture to obtain a-mixture of the refractorymetal and compounds containing the additive materials and thereafterpressing, sintering and mechanically worksinteredV metal to wire form.

14. rlhe method of making non-twist Wire which comprises adding to arefractory metal oxide free from compounds deleteriously affectingcrystal formation, a small amount of a mixture of compounds containingalkali and alkaline earth metals, such as lithium, strontium, calcium orcassiuip, reducing the mixture to obtain a mixture of metal andcompounds containing the additive materials and thereafter pressing,sintering and mechanically working said sintered metal to wire form.

15. The,i method of making non-sag and non-twist lungsten wire whichcomprises adding to tungsten oxide free from deleterious compoundsaffecting crystal growth, a small proportion of a salt of lithium,reducing said mixture to obtain a mixture of tungsten and a compoundcontaining lit ium, sinteringand mechanically working the sintered metalto thel desired size.

16. The method of preparing iilamentary tungsten having a predeterminedcrystal structure, which comprises mixing with tungsten oxide free fromcompounds deleteriously affecting crystal growth, a plurality ofcompounds containing alkali or alkaline earth metals, said compoundsbeing selected lso that the desired crystal structure is promotedthrough the influence of one compound upon another, reducing saidmixture, pressing, `sintering and mechanically working the sinteredmetal to wire. form.

f 17. The method of preparing filamentary tungsten havin a predeterminedcrystal structure, whic comprises mixing with tungsten oxide free fromcompounds deleteriously affecting crystal growth, a plurality ofcompounds containing alkali and alkaline earth metals, said compoundsbeing selected so that the desired crystal structure is promoted throughthe infiuence of 011e compound upon another, reducing said mixture,pressing, sintering and mechanically working the sintered metal to wireform.

18. The method of preparing fllamentary tungsten having non-sag andnon-twist properties which comprises adding to tungstic oxide free fromcompounds deleteriously affecting crystal growth, lithium oxide in theproportion of about .1% by weight, reducing said mixture to obtain amixture of 'tungsten metal and a compound containing,

lithium, sintermg and mechanically Working the sintered metal to about10 mils diameter.

19. A coherent tungsten body having nonsag and non-twist properties andcomprising substantially ypure tungsten having large crystals fairlyregular in shape and size.

20. Tungsten filamentary material capable of resisting sagging andtwisting and comprising substantially pure tungsten having largecrystals fairly regular in shape and size.

2l. A substantially pure tungsten filament having a large grainstructure which renders the filament resistant to sagging and twistingduring a normal or commercially useful life.

22. A substantially pure tungsten filament vhaving a large grainstructure which renders the filament resistant to twisting during anormal or commercially useful life.

23. A 'coiled tungsten filament having non-slag and non-twist propertiesand comprising substantially pure tungsten having large crystals fairlyregular in shape and size. Y

In testimony whereof, I have hereunto subscribed my name this 14th dayof September, 1922.

WILLIAM BENJAinN cfERo.V

